The present invention relates to a plunger pump and more particularly to a plunger pump of the type including a worm for rotating the plunger wherein the worm is not mounted on the pump body.
The plunger pump is intended to suck and deliver fluid by rotational and sliding movement of a plunger within a pump body to open and close a suction port and a delivery port on the plunger.
To rotate the plunger, a worm wheel is formed around the periphery of the plunger or a worm gear is fixedly secured to the periphery of the plunger so that a worm adapted to rotate in association with a crankshaft is brought into meshing engagement with the worm wheel or worm gear. The plunger is adapted to rotate in dependence on the number of revolutions of the crankshaft. So as to allow the plunger to slidably move, the plunger is formed with an end face cam having convexity and concavity and in the pump body is mounted a control cam so that the end face cam of the plunger is normally in contact with the control cam. Owing to the arrangement made in that way, as the plunger is rotated, the plunger slidably moves in the pump body under the effect of the end face cam. Such a plunger pump constructed in the above-described manner is disclosed in U.S. Pat. No. 4,043,711 (corresponding to Japanese Published Pat. No. 25124/1958) or U.S. Pat. No. 4,036,326 (corresponding to Japanese Published Model No. 24374/1980).
Heretofore, rotation of the worm was transmitted from the crankshaft via a speed reduction unit in order to finely adjust a fine flow rate. To this end, a worm shaft is supported on the cylindrical pump body so that the worm meshes with the plunger in the pump body. Accordingly, the pump body is integrally formed with a hump-shaped portion extending at a right angle relative to the direction of sliding movement of the plunger in order to accommodate the worm meshing with the plunger therein, and a hole for holding the worm shaft is formed in the hump-shaped portion. However, the pump body with such a hump-shaped portion integrally formed thereon to hold the worm is difficult to be cast and moreover a long period of time is consumed in precisely machining the plunger and the hole for holding the worm shaft, resulting in the plunger pump being manufactured at an expensive cost.
Adjustment of a flow rate is achieved for a conventional plunger pump by changing the sliding stroke length of the plunger. Specifically, a projection serving as an adjustment cam is provided in the center of an annular end face cam and a control cam face adapted to come in contact with the projection is formed on the peripheral surface at the fore end of a control cam shaft so that the sliding stroke of the plunger is changed by changing the position where the control cam face comes in contact with the projection. This control cam shaft is fitted to the pump body by screw threading and thus the position where the cam surface contacts the projection can be changed by rotating the control cam shaft.
However, due to the fact that the cam surface of the control cam shaft requires high accuracy, manufacturing of the control cam shaft is achieved at an expensive cost. Further, since the stroke of the plunger varies even when the rotational angle of the control cam shaft deviates slightly from its correct position, there is the fear that an exact flow rate can not be obtained.